The present invention relates to methods and apparatus for impregnating tobacco with a gas or its liquid phase, under pressure, in a continuous process with relatively compact and inexpensive equipment, for the purpose of expanding said tobacco.
Numerous processes now exist for expanding tobacco, in which said tobacco is treated with a gas or its liquid phase under pressure at some point in each of said processes. All of these processes are limited to the treatment of batches of tobacco during said pressurized treatment step and therefore require very expensive equipment, and in some cases are not industrially practical, in varying degree.
U.S. Pat. No. 4,165,618 describes a complex system of autoclaves and holding chambers to submerge tobacco in liquid CO.sub.2 at a very high pressure. Subsequently a portion of said liquid CO.sub.2 is removed from said autoclaves, leaving behind that liquid which has impregnated the tobacco. In the commercially available DIET process for expanding tobacco, vessels containing tobacco which has been impregnated with said liquid are than vented to atmospheric pressure so that a portion of said liquid is converted to dry ice within said tobacco. Said tobacco is then heated to rapidly convert said dry ice to gas, to expand said tobacco and to fix it in its expanded condition.
A United Kingdom patent describes a process which is similar in that tobacco is impregnated with liquid CO.sub.2 and then vented to convert said liquid to dry ice, and then heated to effect and fix the expansion of said tobacco. However the initial impregnation of said tobacco with said liquid is performed in this case with a spray of said liquid rather than by submersion.
U.S. Pat. No. 4,250,898 describes a process in which tobacco is impregnated with CO.sub.2 gas under pressure and then chilled to about -90.degree. F. to convert said gas to dry ice within said tobacco. Said dry ice impregnated tobacco is then heated, to effect and fix the expansion of said tobacco.
The process described in U.S. Pat. No. 4,250,898 is inherently a batch process and a cumbersome procedure for industrial application. However it demonstrates that tobacco may be effectively impregnated with CO.sub.2 at a pressure as low as about 50 psig, provided that said impregnation step is controlled and limited, which control is not possible if said tobacco is impregnated by submersion in liquid. This is significant because pressure in this range can practically be achieved and maintained with substantially different and simpler equipment, as compared with higher pressures such as over about 100 psig.
There is still another and more extreme high pressure process in which tobacco is soaked in nitrogen gas at pressures in the order of thousands of psi. When the vessel containing said pressurized tobacco is vented, said tobacco is expanded by decompression. Said tobacco is then heated, but in this case said heating step serves only to fix the already expanded tobacco in its expanded condition. However expansion by this process is dependent upon the pressure differential between the inside and outside of said tobacco during decompression. Said pressure differential is in turn influenced by the rate of decompression, which relatively slow in the venting of a vessel through a valve. The same level of said pressure differential can be obtained with substantially lower initial pressure, provided that the rate of decompression is made very rapid.
Accordingly the prior art exhibits a clear need for a simple and continuous technique incorporating the treatment of tobacco under pressure with a gas or its liquid phase, in order to expand said tobacco.
It is an object of the present invention to provide methods and apparatus, for the impregnation of tobacco under pressure, which are relatively inexpensive, continuous in operation, and relatively convenient in an industrial environment.
It is a further object of the invention to provide flexibility in terms of the type and form of expanding agent to be used.